In the apparatus of the prior art having a cooling fan as the means for cooling a heat generating part such as a power source or a processor, when the temperature increase is detected by a temperature detecting circuit placed in a chassis of the apparatus, the increased temperature is reduced by making a rotational speed of the cooling fan high.
Further, in an electronic device of the prior art, the technique of increasing and reducing the rotational speed of the cooling fan in accordance with an increase and decrease of the number of shelves mounted in the chassis of the electronic device which can mount a lot of electronic circuit packages has been known (for example, refer to Japanese Patent Application Laid-Open No. 6-272694).